Hi Jun,
Thanks a lot for the comments. Please see inline replies.
Thanks,
Jiangjie (Becket) Qin
On Mon, Dec 14, 2015 at 10:19 AM, Jun Rao <j...@confluent.io> wrote:
> Hi, Becket,
>
> Thanks for the proposal. Looks good overall. A few comments below.
>
> 1. KIP-32 didn't say what timestamp should be set in a compressed message.
> We probably should set it to the timestamp of the latest messages included
> in the compressed one. This way, during indexing, we don't have to
> decompress the message.
>
That is a good point.
In normal cases, broker needs to decompress the message for verification
purpose anyway. So building time index does not add additional
decompression.
During time index recovery, however, having a timestamp in compressed
message might save the decompression.
Another thing I am thinking is we should make sure KIP-32 works well with
KIP-31. i.e. we don't want to do recompression in order to add timestamp to
messages.
Take the approach in my last email, the timestamp in the messages will
either all be overwritten by server if
message.timestamp.type=LogAppendTime, or they will not be overwritten if
message.timestamp.type=CreateTime.
Maybe we can use the timestamp in compressed messages in the following way:
If message.timestamp.type=LogAppendTime, we have to overwrite timestamps
for all the messages. We can simply write the timestamp in the compressed
message to avoid recompression.
If message.timestamp.type=CreateTime, we do not need to overwrite the
timestamps. We either reject the entire compressed message or We just leave
the compressed message timestamp to be -1.
So the semantic of the timestamp field in compressed message field becomes:
if it is greater than 0, that means LogAppendTime is used, the timestamp of
the inner messages is the compressed message LogAppendTime. If it is -1,
that means the CreateTime is used, the timestamp is in each individual
inner message.
This sacrifice the speed of recovery but seems worthy because we avoid
recompression.
> 2. In KIP-33, should we make the time-based index interval configurable?
> Perhaps we can default it 60 secs, but allow users to configure it to
> smaller values if they want more precision.
>
Yes, we can do that.
> 3. In KIP-33, I am not sure if log rolling should be based on the earliest
> message. This would mean that we will need to roll a log segment every time
> we get a message delayed by the log rolling time interval. Also, on broker
> startup, we can get the timestamp of the latest message in a log segment
> pretty efficiently by just looking at the last time index entry. But
> getting the timestamp of the earliest timestamp requires a full scan of all
> log segments, which can be expensive. Previously, there were two use cases
> of time-based rolling: (a) more accurate time-based indexing and (b)
> retaining data by time (since the active segment is never deleted). (a) is
> already solved with a time-based index. For (b), if the retention is based
> on the timestamp of the latest message in a log segment, perhaps log
> rolling should be based on that too.
>
I am not sure how to make log rolling work with the latest timestamp in
current log segment. Do you mean the log rolling can based on the last log
segment's latest timestamp? If so how do we roll out the first segment?
> 4. In KIP-33, I presume the timestamp in the time index will be
> monotonically increasing. So, if all messages in a log segment have a
> timestamp less than the largest timestamp in the previous log segment, we
> will use the latter to index this log segment?
>
Yes. The timestamps are monotonically increasing. If the largest timestamp
in the previous segment is very big, it is possible the time index of the
current segment only have two index entries (inserted during segment
creation and roll out), both are pointing to a message in the previous log
segment. This is the corner case I mentioned before that we should expire
the next log segment even before expiring the previous log segment just
because the largest timestamp is in previous log segment. In current
approach, we will wait until the previous log segment expires, and then
delete both the previous log segment and the next log segment.
> 5. In KIP-32, in the wire protocol, we mention both timestamp and time.
> They should be consistent.
>
Will fix the wiki page.
> Jun
>
>
>
> On Thu, Dec 10, 2015 at 10:13 AM, Becket Qin <becket....@gmail.com> wrote:
>
> > Hey Jay,
> >
> > Thanks for the comments.
> >
> > Good point about the actions after when max.message.time.difference is
> > exceeded. Rejection is a useful behavior although I cannot think of use
> > case at LinkedIn at this moment. I think it makes sense to add a
> > configuration.
> >
> > How about the following configurations?
> > 1. message.timestamp.type=CreateTime/LogAppendTime
> > 2. max.message.time.difference.ms
> >
> > if message.timestamp.type is set to CreateTime, when the broker receives
> a
> > message, it will further check max.message.time.difference.ms, and will
> > reject the message it the time difference exceeds the threshold.
> > If message.timestamp.type is set to LogAppendTime, the broker will always
> > stamp the message with current server time, regardless the value of
> > max.message.time.difference.ms
> >
> > This will make sure the message on the broker is either CreateTime or
> > LogAppendTime, but not mixture of both.
> >
> > What do you think?
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> >
> > On Wed, Dec 9, 2015 at 2:42 PM, Jay Kreps <j...@confluent.io> wrote:
> >
> > > Hey Becket,
> > >
> > > That summary of pros and cons sounds about right to me.
> > >
> > > There are potentially two actions you could take when
> > > max.message.time.difference is exceeded--override it or reject the
> > > message entirely. Can we pick one of these or does the action need to
> > > be configurable too? (I'm not sure). The downside of more
> > > configuration is that it is more fiddly and has more modes.
> > >
> > > I suppose the reason I was thinking of this as a "difference" rather
> > > than a hard type was that if you were going to go the reject mode you
> > > would need some tolerance setting (i.e. if your SLA is that if your
> > > timestamp is off by more than 10 minutes I give you an error). I agree
> > > with you that having one field that is potentially containing a mix of
> > > two values is a bit weird.
> > >
> > > -Jay
> > >
> > > On Mon, Dec 7, 2015 at 5:17 PM, Becket Qin <becket....@gmail.com>
> wrote:
> > > > It looks the format of the previous email was messed up. Send it
> again.
> > > >
> > > > Just to recap, the last proposal Jay made (with some implementation
> > > > details added)
> > > > was:
> > > >
> > > > 1. Allow user to stamp the message when produce
> > > >
> > > > 2. When broker receives a message it take a look at the difference
> > > between
> > > > its local time and the timestamp in the message.
> > > > a. If the time difference is within a configurable
> > > > max.message.time.difference.ms, the server will accept it and append
> > it
> > > to
> > > > the log.
> > > > b. If the time difference is beyond the configured
> > > > max.message.time.difference.ms, the server will override the
> timestamp
> > > with
> > > > its current local time and append the message to the log.
> > > > c. The default value of max.message.time.difference would be set to
> > > > Long.MaxValue.
> > > >
> > > > 3. The configurable time difference threshold
> > > > max.message.time.difference.ms will
> > > > be a per topic configuration.
> > > >
> > > > 4. The indexed will be built so it has the following guarantee.
> > > > a. If user search by time stamp:
> > > > - all the messages after that timestamp will be consumed.
> > > > - user might see earlier messages.
> > > > b. The log retention will take a look at the last time index entry
> in
> > > the
> > > > time index file. Because the last entry will be the latest timestamp
> in
> > > the
> > > > entire log segment. If that entry expires, the log segment will be
> > > deleted.
> > > > c. The log rolling has to depend on the earliest timestamp. In this
> > > case
> > > > we may need to keep a in memory timestamp only for the current active
> > > log.
> > > > On recover, we will need to read the active log segment to get this
> > > timestamp
> > > > of the earliest messages.
> > > >
> > > > 5. The downside of this proposal are:
> > > > a. The timestamp might not be monotonically increasing.
> > > > b. The log retention might become non-deterministic. i.e. When a
> > > message
> > > > will be deleted now depends on the timestamp of the other messages in
> > the
> > > > same log segment. And those timestamps are provided by
> > > > user within a range depending on what the time difference threshold
> > > > configuration is.
> > > > c. The semantic meaning of the timestamp in the messages could be a
> > > little
> > > > bit vague because some of them come from the producer and some of
> them
> > > are
> > > > overwritten by brokers.
> > > >
> > > > 6. Although the proposal has some downsides, it gives user the
> > > flexibility
> > > > to use the timestamp.
> > > > a. If the threshold is set to Long.MaxValue. The timestamp in the
> > > message is
> > > > equivalent to CreateTime.
> > > > b. If the threshold is set to 0. The timestamp in the message is
> > > equivalent
> > > > to LogAppendTime.
> > > >
> > > > This proposal actually allows user to use either CreateTime or
> > > LogAppendTime
> > > > without introducing two timestamp concept at the same time. I have
> > > updated
> > > > the wiki for KIP-32 and KIP-33 with this proposal.
> > > >
> > > > One thing I am thinking is that instead of having a time difference
> > > threshold,
> > > > should we simply set have a TimestampType configuration? Because in
> > most
> > > > cases, people will either set the threshold to 0 or Long.MaxValue.
> > > Setting
> > > > anything in between will make the timestamp in the message
> meaningless
> > to
> > > > user - user don't know if the timestamp has been overwritten by the
> > > brokers.
> > > >
> > > > Any thoughts?
> > > >
> > > > Thanks,
> > > > Jiangjie (Becket) Qin
> > > >
> > > > On Mon, Dec 7, 2015 at 10:33 AM, Jiangjie Qin
> > <j...@linkedin.com.invalid
> > > >
> > > > wrote:
> > > >
> > > >> Bump up this thread.
> > > >>
> > > >> Just to recap, the last proposal Jay made (with some implementation
> > > details
> > > >> added) was:
> > > >>
> > > >> 1. Allow user to stamp the message when produce
> > > >> 2. When broker receives a message it take a look at the
> difference
> > > >> between its local time and the timestamp in the message.
> > > >> - If the time difference is within a configurable
> > > >> max.message.time.difference.ms, the server will accept it and
> > > append
> > > >> it to the log.
> > > >> - If the time difference is beyond the configured
> > > >> max.message.time.difference.ms, the server will override the
> > > >> timestamp with its current local time and append the message
> to
> > > the
> > > >> log.
> > > >> - The default value of max.message.time.difference would be
> set
> > to
> > > >> Long.MaxValue.
> > > >> 3. The configurable time difference threshold
> > > >> max.message.time.difference.ms will be a per topic
> configuration.
> > > >> 4. The indexed will be built so it has the following guarantee.
> > > >> - If user search by time stamp:
> > > >> - all the messages after that timestamp will be consumed.
> > > >> - user might see earlier messages.
> > > >> - The log retention will take a look at the last time index
> > entry
> > > in
> > > >> the time index file. Because the last entry will be the latest
> > > >> timestamp in
> > > >> the entire log segment. If that entry expires, the log segment
> > > will
> > > >> be
> > > >> deleted.
> > > >> - The log rolling has to depend on the earliest timestamp. In
> > this
> > > >> case we may need to keep a in memory timestamp only for the
> > > >> current active
> > > >> log. On recover, we will need to read the active log segment
> to
> > > get
> > > >> this
> > > >> timestamp of the earliest messages.
> > > >> 5. The downside of this proposal are:
> > > >> - The timestamp might not be monotonically increasing.
> > > >> - The log retention might become non-deterministic. i.e. When
> a
> > > >> message will be deleted now depends on the timestamp of the
> > > >> other messages
> > > >> in the same log segment. And those timestamps are provided by
> > > >> user within a
> > > >> range depending on what the time difference threshold
> > > configuration
> > > >> is.
> > > >> - The semantic meaning of the timestamp in the messages could
> > be a
> > > >> little bit vague because some of them come from the producer
> and
> > > >> some of
> > > >> them are overwritten by brokers.
> > > >> 6. Although the proposal has some downsides, it gives user the
> > > >> flexibility to use the timestamp.
> > > >> - If the threshold is set to Long.MaxValue. The timestamp in the
> > > message
> > > >> is equivalent to CreateTime.
> > > >> - If the threshold is set to 0. The timestamp in the message
> is
> > > >> equivalent to LogAppendTime.
> > > >>
> > > >> This proposal actually allows user to use either CreateTime or
> > > >> LogAppendTime without introducing two timestamp concept at the same
> > > time. I
> > > >> have updated the wiki for KIP-32 and KIP-33 with this proposal.
> > > >>
> > > >> One thing I am thinking is that instead of having a time difference
> > > >> threshold, should we simply set have a TimestampType configuration?
> > > Because
> > > >> in most cases, people will either set the threshold to 0 or
> > > Long.MaxValue.
> > > >> Setting anything in between will make the timestamp in the message
> > > >> meaningless to user - user don't know if the timestamp has been
> > > overwritten
> > > >> by the brokers.
> > > >>
> > > >> Any thoughts?
> > > >>
> > > >> Thanks,
> > > >> Jiangjie (Becket) Qin
> > > >>
> > > >> On Mon, Oct 26, 2015 at 1:23 PM, Jiangjie Qin <j...@linkedin.com>
> > > wrote:
> > > >>
> > > >> > Hi Jay,
> > > >> >
> > > >> > Thanks for such detailed explanation. I think we both are trying
> to
> > > make
> > > >> > CreateTime work for us if possible. To me by "work" it means clear
> > > >> > guarantees on:
> > > >> > 1. Log Retention Time enforcement.
> > > >> > 2. Log Rolling time enforcement (This might be less a concern as
> you
> > > >> > pointed out)
> > > >> > 3. Application search message by time.
> > > >> >
> > > >> > WRT (1), I agree the expectation for log retention might be
> > different
> > > >> > depending on who we ask. But my concern is about the level of
> > > guarantee
> > > >> we
> > > >> > give to user. My observation is that a clear guarantee to user is
> > > >> critical
> > > >> > regardless of the mechanism we choose. And this is the subtle but
> > > >> important
> > > >> > difference between using LogAppendTime and CreateTime.
> > > >> >
> > > >> > Let's say user asks this question: How long will my message stay
> in
> > > >> Kafka?
> > > >> >
> > > >> > If we use LogAppendTime for log retention, the answer is message
> > will
> > > >> stay
> > > >> > in Kafka for retention time after the message is produced (to be
> > more
> > > >> > precise, upper bounded by log.rolling.ms + log.retention.ms).
> User
> > > has a
> > > >> > clear guarantee and they may decide whether or not to put the
> > message
> > > >> into
> > > >> > Kafka. Or how to adjust the retention time according to their
> > > >> requirements.
> > > >> > If we use create time for log retention, the answer would be it
> > > depends.
> > > >> > The best answer we can give is at least retention.ms because
> there
> > > is no
> > > >> > guarantee when the messages will be deleted after that. If a
> message
> > > sits
> > > >> > somewhere behind a larger create time, the message might stay
> longer
> > > than
> > > >> > expected. But we don't know how longer it would be because it
> > depends
> > > on
> > > >> > the create time. In this case, it is hard for user to decide what
> to
> > > do.
> > > >> >
> > > >> > I am worrying about this because a blurring guarantee has bitten
> us
> > > >> > before, e.g. Topic creation. We have received many questions like
> > > "why my
> > > >> > topic is not there after I created it". I can imagine we receive
> > > similar
> > > >> > question asking "why my message is still there after retention
> time
> > > has
> > > >> > reached". So my understanding is that a clear and solid guarantee
> is
> > > >> better
> > > >> > than having a mechanism that works in most cases but occasionally
> > does
> > > >> not
> > > >> > work.
> > > >> >
> > > >> > If we think of the retention guarantee we provide with
> > LogAppendTime,
> > > it
> > > >> > is not broken as you said, because we are telling user the log
> > > retention
> > > >> is
> > > >> > NOT based on create time at the first place.
> > > >> >
> > > >> > WRT (3), no matter whether we index on LogAppendTime or
> CreateTime,
> > > the
> > > >> > best guarantee we can provide with user is "not missing message
> > after
> > > a
> > > >> > certain timestamp". Therefore I actually really like to index on
> > > >> CreateTime
> > > >> > because that is the timestamp we provide to user, and we can have
> > the
> > > >> solid
> > > >> > guarantee.
> > > >> > On the other hand, indexing on LogAppendTime and giving user
> > > CreateTime
> > > >> > does not provide solid guarantee when user do search based on
> > > timestamp.
> > > >> It
> > > >> > only works when LogAppendTime is always no earlier than
> CreateTime.
> > > This
> > > >> is
> > > >> > a reasonable assumption and we can easily enforce it.
> > > >> >
> > > >> > With above, I am not sure if we can avoid server timestamp to make
> > log
> > > >> > retention work with a clear guarantee. For searching by timestamp
> > use
> > > >> case,
> > > >> > I really want to have the index built on CreateTime. But with a
> > > >> reasonable
> > > >> > assumption and timestamp enforcement, a LogAppendTime index would
> > also
> > > >> work.
> > > >> >
> > > >> > Thanks,
> > > >> >
> > > >> > Jiangjie (Becket) Qin
> > > >> >
> > > >> >
> > > >> >
> > > >> > On Thu, Oct 22, 2015 at 10:48 AM, Jay Kreps <j...@confluent.io>
> > wrote:
> > > >> >
> > > >> >> Hey Becket,
> > > >> >>
> > > >> >> Let me see if I can address your concerns:
> > > >> >>
> > > >> >> 1. Let's say we have two source clusters that are mirrored to the
> > > same
> > > >> >> > target cluster. For some reason one of the mirror maker from a
> > > cluster
> > > >> >> dies
> > > >> >> > and after fix the issue we want to resume mirroring. In this
> case
> > > it
> > > >> is
> > > >> >> > possible that when the mirror maker resumes mirroring, the
> > > timestamp
> > > >> of
> > > >> >> the
> > > >> >> > messages have already gone beyond the acceptable timestamp
> range
> > on
> > > >> >> broker.
> > > >> >> > In order to let those messages go through, we have to bump up
> the
> > > >> >> > *max.append.delay
> > > >> >> > *for all the topics on the target broker. This could be
> painful.
> > > >> >>
> > > >> >>
> > > >> >> Actually what I was suggesting was different. Here is my
> > observation:
> > > >> >> clusters/topics directly produced to by applications have a valid
> > > >> >> assertion
> > > >> >> that log append time and create time are similar (let's call
> these
> > > >> >> "unbuffered"); other cluster/topic such as those that receive
> data
> > > from
> > > >> a
> > > >> >> database, a log file, or another kafka cluster don't have that
> > > >> assertion,
> > > >> >> for these "buffered" clusters data can be arbitrarily late. This
> > > means
> > > >> any
> > > >> >> use of log append time on these buffered clusters is not very
> > > >> meaningful,
> > > >> >> and create time and log append time "should" be similar on
> > unbuffered
> > > >> >> clusters so you can probably use either.
> > > >> >>
> > > >> >> Using log append time on buffered clusters actually results in
> bad
> > > >> things.
> > > >> >> If you request the offset for a given time you get don't end up
> > > getting
> > > >> >> data for that time but rather data that showed up at that time.
> If
> > > you
> > > >> try
> > > >> >> to retain 7 days of data it may mostly work but any kind of
> > > >> bootstrapping
> > > >> >> will result in retaining much more (potentially the whole
> database
> > > >> >> contents!).
> > > >> >>
> > > >> >> So what I am suggesting in terms of the use of the
> max.append.delay
> > > is
> > > >> >> that
> > > >> >> unbuffered clusters would have this set and buffered clusters
> would
> > > not.
> > > >> >> In
> > > >> >> other words, in LI terminology, tracking and metrics clusters
> would
> > > have
> > > >> >> this enforced, aggregate and replica clusters wouldn't.
> > > >> >>
> > > >> >> So you DO have the issue of potentially maintaining more data
> than
> > > you
> > > >> >> need
> > > >> >> to on aggregate clusters if your mirroring skews, but you DON'T
> > need
> > > to
> > > >> >> tweak the setting as you described.
> > > >> >>
> > > >> >> 2. Let's say in the above scenario we let the messages in, at
> that
> > > point
> > > >> >> > some log segments in the target cluster might have a wide range
> > of
> > > >> >> > timestamps, like Guozhang mentioned the log rolling could be
> > tricky
> > > >> >> because
> > > >> >> > the first time index entry does not necessarily have the
> smallest
> > > >> >> timestamp
> > > >> >> > of all the messages in the log segment. Instead, it is the
> > largest
> > > >> >> > timestamp ever seen. We have to scan the entire log to find the
> > > >> message
> > > >> >> > with smallest offset to see if we should roll.
> > > >> >>
> > > >> >>
> > > >> >> I think there are two uses for time-based log rolling:
> > > >> >> 1. Making the offset lookup by timestamp work
> > > >> >> 2. Ensuring we don't retain data indefinitely if it is supposed
> to
> > > get
> > > >> >> purged after 7 days
> > > >> >>
> > > >> >> But think about these two use cases. (1) is totally obviated by
> the
> > > >> >> time=>offset index we are adding which yields much more granular
> > > offset
> > > >> >> lookups. (2) Is actually totally broken if you switch to append
> > time,
> > > >> >> right? If you want to be sure for security/privacy reasons you
> only
> > > >> retain
> > > >> >> 7 days of data then if the log append and create time diverge you
> > > >> actually
> > > >> >> violate this requirement.
> > > >> >>
> > > >> >> I think 95% of people care about (1) which is solved in the
> > proposal
> > > and
> > > >> >> (2) is actually broken today as well as in both proposals.
> > > >> >>
> > > >> >> 3. Theoretically it is possible that an older log segment
> contains
> > > >> >> > timestamps that are older than all the messages in a newer log
> > > >> segment.
> > > >> >> It
> > > >> >> > would be weird that we are supposed to delete the newer log
> > segment
> > > >> >> before
> > > >> >> > we delete the older log segment.
> > > >> >>
> > > >> >>
> > > >> >> The index timestamps would always be a lower bound (i.e. the
> > maximum
> > > at
> > > >> >> that time) so I don't think that is possible.
> > > >> >>
> > > >> >> 4. In bootstrap case, if we reload the data to a Kafka cluster,
> we
> > > have
> > > >> >> to
> > > >> >> > make sure we configure the topic correctly before we load the
> > data.
> > > >> >> > Otherwise the message might either be rejected because the
> > > timestamp
> > > >> is
> > > >> >> too
> > > >> >> > old, or it might be deleted immediately because the retention
> > time
> > > has
> > > >> >> > reached.
> > > >> >>
> > > >> >>
> > > >> >> See (1).
> > > >> >>
> > > >> >> -Jay
> > > >> >>
> > > >> >> On Tue, Oct 13, 2015 at 7:30 PM, Jiangjie Qin
> > > <j...@linkedin.com.invalid
> > > >> >
> > > >> >> wrote:
> > > >> >>
> > > >> >> > Hey Jay and Guozhang,
> > > >> >> >
> > > >> >> > Thanks a lot for the reply. So if I understand correctly, Jay's
> > > >> proposal
> > > >> >> > is:
> > > >> >> >
> > > >> >> > 1. Let client stamp the message create time.
> > > >> >> > 2. Broker build index based on client-stamped message create
> > time.
> > > >> >> > 3. Broker only takes message whose create time is withing
> current
> > > time
> > > >> >> > plus/minus T (T is a configuration *max.append.delay*, could be
> > > topic
> > > >> >> level
> > > >> >> > configuration), if the timestamp is out of this range, broker
> > > rejects
> > > >> >> the
> > > >> >> > message.
> > > >> >> > 4. Because the create time of messages can be out of order,
> when
> > > >> broker
> > > >> >> > builds the time based index it only provides the guarantee that
> > if
> > > a
> > > >> >> > consumer starts consuming from the offset returned by searching
> > by
> > > >> >> > timestamp t, they will not miss any message created after t,
> but
> > > might
> > > >> >> see
> > > >> >> > some messages created before t.
> > > >> >> >
> > > >> >> > To build the time based index, every time when a broker needs
> to
> > > >> insert
> > > >> >> a
> > > >> >> > new time index entry, the entry would be
> > > {Largest_Timestamp_Ever_Seen
> > > >> ->
> > > >> >> > Current_Offset}. This basically means any timestamp larger than
> > the
> > > >> >> > Largest_Timestamp_Ever_Seen must come after this offset because
> > it
> > > >> never
> > > >> >> > saw them before. So we don't miss any message with larger
> > > timestamp.
> > > >> >> >
> > > >> >> > (@Guozhang, in this case, for log retention we only need to
> take
> > a
> > > >> look
> > > >> >> at
> > > >> >> > the last time index entry, because it must be the largest
> > timestamp
> > > >> >> ever,
> > > >> >> > if that timestamp is overdue, we can safely delete any log
> > segment
> > > >> >> before
> > > >> >> > that. So we don't need to scan the log segment file for log
> > > retention)
> > > >> >> >
> > > >> >> > I assume that we are still going to have the new FetchRequest
> to
> > > allow
> > > >> >> the
> > > >> >> > time index replication for replicas.
> > > >> >> >
> > > >> >> > I think Jay's main point here is that we don't want to have two
> > > >> >> timestamp
> > > >> >> > concepts in Kafka, which I agree is a reasonable concern. And I
> > > also
> > > >> >> agree
> > > >> >> > that create time is more meaningful than LogAppendTime for
> users.
> > > But
> > > >> I
> > > >> >> am
> > > >> >> > not sure if making everything base on Create Time would work in
> > all
> > > >> >> cases.
> > > >> >> > Here are my questions about this approach:
> > > >> >> >
> > > >> >> > 1. Let's say we have two source clusters that are mirrored to
> the
> > > same
> > > >> >> > target cluster. For some reason one of the mirror maker from a
> > > cluster
> > > >> >> dies
> > > >> >> > and after fix the issue we want to resume mirroring. In this
> case
> > > it
> > > >> is
> > > >> >> > possible that when the mirror maker resumes mirroring, the
> > > timestamp
> > > >> of
> > > >> >> the
> > > >> >> > messages have already gone beyond the acceptable timestamp
> range
> > on
> > > >> >> broker.
> > > >> >> > In order to let those messages go through, we have to bump up
> the
> > > >> >> > *max.append.delay
> > > >> >> > *for all the topics on the target broker. This could be
> painful.
> > > >> >> >
> > > >> >> > 2. Let's say in the above scenario we let the messages in, at
> > that
> > > >> point
> > > >> >> > some log segments in the target cluster might have a wide range
> > of
> > > >> >> > timestamps, like Guozhang mentioned the log rolling could be
> > tricky
> > > >> >> because
> > > >> >> > the first time index entry does not necessarily have the
> smallest
> > > >> >> timestamp
> > > >> >> > of all the messages in the log segment. Instead, it is the
> > largest
> > > >> >> > timestamp ever seen. We have to scan the entire log to find the
> > > >> message
> > > >> >> > with smallest offset to see if we should roll.
> > > >> >> >
> > > >> >> > 3. Theoretically it is possible that an older log segment
> > contains
> > > >> >> > timestamps that are older than all the messages in a newer log
> > > >> segment.
> > > >> >> It
> > > >> >> > would be weird that we are supposed to delete the newer log
> > segment
> > > >> >> before
> > > >> >> > we delete the older log segment.
> > > >> >> >
> > > >> >> > 4. In bootstrap case, if we reload the data to a Kafka cluster,
> > we
> > > >> have
> > > >> >> to
> > > >> >> > make sure we configure the topic correctly before we load the
> > data.
> > > >> >> > Otherwise the message might either be rejected because the
> > > timestamp
> > > >> is
> > > >> >> too
> > > >> >> > old, or it might be deleted immediately because the retention
> > time
> > > has
> > > >> >> > reached.
> > > >> >> >
> > > >> >> > I am very concerned about the operational overhead and the
> > > ambiguity
> > > >> of
> > > >> >> > guarantees we introduce if we purely rely on CreateTime.
> > > >> >> >
> > > >> >> > It looks to me that the biggest issue of adopting CreateTime
> > > >> everywhere
> > > >> >> is
> > > >> >> > CreateTime can have big gaps. These gaps could be caused by
> > several
> > > >> >> cases:
> > > >> >> > [1]. Faulty clients
> > > >> >> > [2]. Natural delays from different source
> > > >> >> > [3]. Bootstrap
> > > >> >> > [4]. Failure recovery
> > > >> >> >
> > > >> >> > Jay's alternative proposal solves [1], perhaps solve [2] as
> well
> > > if we
> > > >> >> are
> > > >> >> > able to set a reasonable max.append.delay. But it does not seem
> > > >> address
> > > >> >> [3]
> > > >> >> > and [4]. I actually doubt if [3] and [4] are solvable because
> it
> > > looks
> > > >> >> the
> > > >> >> > CreateTime gap is unavoidable in those two cases.
> > > >> >> >
> > > >> >> > Thanks,
> > > >> >> >
> > > >> >> > Jiangjie (Becket) Qin
> > > >> >> >
> > > >> >> >
> > > >> >> > On Tue, Oct 13, 2015 at 3:23 PM, Guozhang Wang <
> > wangg...@gmail.com
> > > >
> > > >> >> wrote:
> > > >> >> >
> > > >> >> > > Just to complete Jay's option, here is my understanding:
> > > >> >> > >
> > > >> >> > > 1. For log retention: if we want to remove data before time
> t,
> > we
> > > >> look
> > > >> >> > into
> > > >> >> > > the index file of each segment and find the largest timestamp
> > t'
> > > <
> > > >> t,
> > > >> >> > find
> > > >> >> > > the corresponding timestamp and start scanning to the end of
> > the
> > > >> >> segment,
> > > >> >> > > if there is no entry with timestamp >= t, we can delete this
> > > >> segment;
> > > >> >> if
> > > >> >> > a
> > > >> >> > > segment's index smallest timestamp is larger than t, we can
> > skip
> > > >> that
> > > >> >> > > segment.
> > > >> >> > >
> > > >> >> > > 2. For log rolling: if we want to start a new segment after
> > time
> > > t,
> > > >> we
> > > >> >> > look
> > > >> >> > > into the active segment's index file, if the largest
> timestamp
> > is
> > > >> >> > already >
> > > >> >> > > t, we can roll a new segment immediately; if it is < t, we
> read
> > > its
> > > >> >> > > corresponding offset and start scanning to the end of the
> > > segment,
> > > >> if
> > > >> >> we
> > > >> >> > > find a record whose timestamp > t, we can roll a new segment.
> > > >> >> > >
> > > >> >> > > For log rolling we only need to possibly scan a small portion
> > the
> > > >> >> active
> > > >> >> > > segment, which should be fine; for log retention we may in
> the
> > > worst
> > > >> >> case
> > > >> >> > > end up scanning all segments, but in practice we may skip
> most
> > of
> > > >> them
> > > >> >> > > since their smallest timestamp in the index file is larger
> than
> > > t.
> > > >> >> > >
> > > >> >> > > Guozhang
> > > >> >> > >
> > > >> >> > >
> > > >> >> > > On Tue, Oct 13, 2015 at 12:52 AM, Jay Kreps <
> j...@confluent.io>
> > > >> wrote:
> > > >> >> > >
> > > >> >> > > > I think it should be possible to index out-of-order
> > timestamps.
> > > >> The
> > > >> >> > > > timestamp index would be similar to the offset index, a
> > memory
> > > >> >> mapped
> > > >> >> > > file
> > > >> >> > > > appended to as part of the log append, but would have the
> > > format
> > > >> >> > > > timestamp offset
> > > >> >> > > > The timestamp entries would be monotonic and as with the
> > offset
> > > >> >> index
> > > >> >> > > would
> > > >> >> > > > be no more often then every 4k (or some configurable
> > threshold
> > > to
> > > >> >> keep
> > > >> >> > > the
> > > >> >> > > > index small--actually for timestamp it could probably be
> much
> > > more
> > > >> >> > sparse
> > > >> >> > > > than 4k).
> > > >> >> > > >
> > > >> >> > > > A search for a timestamp t yields an offset o before which
> no
> > > >> prior
> > > >> >> > > message
> > > >> >> > > > has a timestamp >= t. In other words if you read the log
> > > starting
> > > >> >> with
> > > >> >> > o
> > > >> >> > > > you are guaranteed not to miss any messages occurring at t
> or
> > > >> later
> > > >> >> > > though
> > > >> >> > > > you may get many before t (due to out-of-orderness). Unlike
> > the
> > > >> >> offset
> > > >> >> > > > index this bound doesn't really have to be tight (i.e.
> > > probably no
> > > >> >> need
> > > >> >> > > to
> > > >> >> > > > go search the log itself, though you could).
> > > >> >> > > >
> > > >> >> > > > -Jay
> > > >> >> > > >
> > > >> >> > > > On Tue, Oct 13, 2015 at 12:32 AM, Jay Kreps <
> > j...@confluent.io>
> > > >> >> wrote:
> > > >> >> > > >
> > > >> >> > > > > Here's my basic take:
> > > >> >> > > > > - I agree it would be nice to have a notion of time baked
> > in
> > > if
> > > >> it
> > > >> >> > were
> > > >> >> > > > > done right
> > > >> >> > > > > - All the proposals so far seem pretty complex--I think
> > they
> > > >> might
> > > >> >> > make
> > > >> >> > > > > things worse rather than better overall
> > > >> >> > > > > - I think adding 2x8 byte timestamps to the message is
> > > probably
> > > >> a
> > > >> >> > > > > non-starter from a size perspective
> > > >> >> > > > > - Even if it isn't in the message, having two notions of
> > time
> > > >> that
> > > >> >> > > > control
> > > >> >> > > > > different things is a bit confusing
> > > >> >> > > > > - The mechanics of basing retention etc on log append
> time
> > > when
> > > >> >> > that's
> > > >> >> > > > not
> > > >> >> > > > > in the log seem complicated
> > > >> >> > > > >
> > > >> >> > > > > To that end here is a possible 4th option. Let me know
> what
> > > you
> > > >> >> > think.
> > > >> >> > > > >
> > > >> >> > > > > The basic idea is that the message creation time is
> closest
> > > to
> > > >> >> what
> > > >> >> > the
> > > >> >> > > > > user actually cares about but is dangerous if set wrong.
> So
> > > >> rather
> > > >> >> > than
> > > >> >> > > > > substitute another notion of time, let's try to ensure
> the
> > > >> >> > correctness
> > > >> >> > > of
> > > >> >> > > > > message creation time by preventing arbitrarily bad
> message
> > > >> >> creation
> > > >> >> > > > times.
> > > >> >> > > > >
> > > >> >> > > > > First, let's see if we can agree that log append time is
> > not
> > > >> >> > something
> > > >> >> > > > > anyone really cares about but rather an implementation
> > > detail.
> > > >> The
> > > >> >> > > > > timestamp that matters to the user is when the message
> > > occurred
> > > >> >> (the
> > > >> >> > > > > creation time). The log append time is basically just an
> > > >> >> > approximation
> > > >> >> > > to
> > > >> >> > > > > this on the assumption that the message creation and the
> > > message
> > > >> >> > > receive
> > > >> >> > > > on
> > > >> >> > > > > the server occur pretty close together and the reason to
> > > prefer
> > > >> .
> > > >> >> > > > >
> > > >> >> > > > > But as these values diverge the issue starts to become
> > > apparent.
> > > >> >> Say
> > > >> >> > > you
> > > >> >> > > > > set the retention to one week and then mirror data from a
> > > topic
> > > >> >> > > > containing
> > > >> >> > > > > two years of retention. Your intention is clearly to keep
> > the
> > > >> last
> > > >> >> > > week,
> > > >> >> > > > > but because the mirroring is appending right now you will
> > > keep
> > > >> two
> > > >> >> > > years.
> > > >> >> > > > >
> > > >> >> > > > > The reason we are liking log append time is because we
> are
> > > >> >> > > (justifiably)
> > > >> >> > > > > concerned that in certain situations the creation time
> may
> > > not
> > > >> be
> > > >> >> > > > > trustworthy. This same problem exists on the servers but
> > > there
> > > >> are
> > > >> >> > > fewer
> > > >> >> > > > > servers and they just run the kafka code so it is less of
> > an
> > > >> >> issue.
> > > >> >> > > > >
> > > >> >> > > > > There are two possible ways to handle this:
> > > >> >> > > > >
> > > >> >> > > > > 1. Just tell people to add size based retention. I
> think
> > > this
> > > >> >> is
> > > >> >> > not
> > > >> >> > > > > entirely unreasonable, we're basically saying we
> retain
> > > data
> > > >> >> based
> > > >> >> > > on
> > > >> >> > > > the
> > > >> >> > > > > timestamp you give us in the data. If you give us bad
> > > data we
> > > >> >> will
> > > >> >> > > > retain
> > > >> >> > > > > it for a bad amount of time. If you want to ensure we
> > > don't
> > > >> >> retain
> > > >> >> > > > "too
> > > >> >> > > > > much" data, define "too much" by setting a time-based
> > > >> retention
> > > >> >> > > > setting.
> > > >> >> > > > > This is not entirely unreasonable but kind of suffers
> > > from a
> > > >> >> "one
> > > >> >> > > bad
> > > >> >> > > > > apple" problem in a very large environment.
> > > >> >> > > > > 2. Prevent bad timestamps. In general we can't say a
> > > >> timestamp
> > > >> >> is
> > > >> >> > > bad.
> > > >> >> > > > > However the definition we're implicitly using is that
> we
> > > >> think
> > > >> >> > there
> > > >> >> > > > are a
> > > >> >> > > > > set of topics/clusters where the creation timestamp
> > should
> > > >> >> always
> > > >> >> > be
> > > >> >> > > > "very
> > > >> >> > > > > close" to the log append timestamp. This is true for
> > data
> > > >> >> sources
> > > >> >> > > > that have
> > > >> >> > > > > no buffering capability (which at LinkedIn is very
> > common,
> > > >> but
> > > >> >> is
> > > >> >> > > > more rare
> > > >> >> > > > > elsewhere). The solution in this case would be to
> allow
> > a
> > > >> >> setting
> > > >> >> > > > along the
> > > >> >> > > > > lines of max.append.delay which checks the creation
> > > timestamp
> > > >> >> > > against
> > > >> >> > > > the
> > > >> >> > > > > server time to look for too large a divergence. The
> > > solution
> > > >> >> would
> > > >> >> > > > either
> > > >> >> > > > > be to reject the message or to override it with the
> > server
> > > >> >> time.
> > > >> >> > > > >
> > > >> >> > > > > So in LI's environment you would configure the clusters
> > used
> > > for
> > > >> >> > > direct,
> > > >> >> > > > > unbuffered, message production (e.g. tracking and metrics
> > > local)
> > > >> >> to
> > > >> >> > > > enforce
> > > >> >> > > > > a reasonably aggressive timestamp bound (say 10 mins),
> and
> > > all
> > > >> >> other
> > > >> >> > > > > clusters would just inherent these.
> > > >> >> > > > >
> > > >> >> > > > > The downside of this approach is requiring the special
> > > >> >> configuration.
> > > >> >> > > > > However I think in 99% of environments this could be
> > skipped
> > > >> >> > entirely,
> > > >> >> > > > it's
> > > >> >> > > > > only when the ratio of clients to servers gets so massive
> > > that
> > > >> you
> > > >> >> > need
> > > >> >> > > > to
> > > >> >> > > > > do this. The primary upside is that you have a single
> > > >> >> authoritative
> > > >> >> > > > notion
> > > >> >> > > > > of time which is closest to what a user would want and is
> > > stored
> > > >> >> > > directly
> > > >> >> > > > > in the message.
> > > >> >> > > > >
> > > >> >> > > > > I'm also assuming there is a workable approach for
> indexing
> > > >> >> > > non-monotonic
> > > >> >> > > > > timestamps, though I haven't actually worked that out.
> > > >> >> > > > >
> > > >> >> > > > > -Jay
> > > >> >> > > > >
> > > >> >> > > > > On Mon, Oct 5, 2015 at 8:52 PM, Jiangjie Qin
> > > >> >> > <j...@linkedin.com.invalid
> > > >> >> > > >
> > > >> >> > > > > wrote:
> > > >> >> > > > >
> > > >> >> > > > >> Bumping up this thread although most of the discussion
> > were
> > > on
> > > >> >> the
> > > >> >> > > > >> discussion thread of KIP-31 :)
> > > >> >> > > > >>
> > > >> >> > > > >> I just updated the KIP page to add detailed solution for
> > the
> > > >> >> option
> > > >> >> > > > >> (Option
> > > >> >> > > > >> 3) that does not expose the LogAppendTime to user.
> > > >> >> > > > >>
> > > >> >> > > > >>
> > > >> >> > > > >>
> > > >> >> > > >
> > > >> >> > >
> > > >> >> >
> > > >> >>
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-32+-+Add+CreateTime+and+LogAppendTime+to+Kafka+message
> > > >> >> > > > >>
> > > >> >> > > > >> The option has a minor change to the fetch request to
> > allow
> > > >> >> fetching
> > > >> >> > > > time
> > > >> >> > > > >> index entry as well. I kind of like this solution
> because
> > > its
> > > >> >> just
> > > >> >> > > doing
> > > >> >> > > > >> what we need without introducing other things.
> > > >> >> > > > >>
> > > >> >> > > > >> It will be great to see what are the feedback. I can
> > explain
> > > >> more
> > > >> >> > > during
> > > >> >> > > > >> tomorrow's KIP hangout.
> > > >> >> > > > >>
> > > >> >> > > > >> Thanks,
> > > >> >> > > > >>
> > > >> >> > > > >> Jiangjie (Becket) Qin
> > > >> >> > > > >>
> > > >> >> > > > >> On Thu, Sep 10, 2015 at 2:47 PM, Jiangjie Qin <
> > > >> j...@linkedin.com
> > > >> >> >
> > > >> >> > > > wrote:
> > > >> >> > > > >>
> > > >> >> > > > >> > Hi Jay,
> > > >> >> > > > >> >
> > > >> >> > > > >> > I just copy/pastes here your feedback on the timestamp
> > > >> proposal
> > > >> >> > that
> > > >> >> > > > was
> > > >> >> > > > >> > in the discussion thread of KIP-31. Please see the
> > replies
> > > >> >> inline.
> > > >> >> > > > >> > The main change I made compared with previous proposal
> > is
> > > to
> > > >> >> add
> > > >> >> > > both
> > > >> >> > > > >> > CreateTime and LogAppendTime to the message.
> > > >> >> > > > >> >
> > > >> >> > > > >> > On Tue, Sep 8, 2015 at 10:57 AM, Jay Kreps <
> > > j...@confluent.io
> > > >> >
> > > >> >> > > wrote:
> > > >> >> > > > >> >
> > > >> >> > > > >> > > Hey Beckett,
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > I was proposing splitting up the KIP just for
> > > simplicity of
> > > >> >> > > > >> discussion.
> > > >> >> > > > >> > You
> > > >> >> > > > >> > > can still implement them in one patch. I think
> > > otherwise it
> > > >> >> will
> > > >> >> > > be
> > > >> >> > > > >> hard
> > > >> >> > > > >> > to
> > > >> >> > > > >> > > discuss/vote on them since if you like the offset
> > > proposal
> > > >> >> but
> > > >> >> > not
> > > >> >> > > > the
> > > >> >> > > > >> > time
> > > >> >> > > > >> > > proposal what do you do?
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > Introducing a second notion of time into Kafka is a
> > > pretty
> > > >> >> > massive
> > > >> >> > > > >> > > philosophical change so it kind of warrants it's own
> > > KIP I
> > > >> >> think
> > > >> >> > > it
> > > >> >> > > > >> > isn't
> > > >> >> > > > >> > > just "Change message format".
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > WRT time I think one thing to clarify in the
> proposal
> > is
> > > >> how
> > > >> >> MM
> > > >> >> > > will
> > > >> >> > > > >> have
> > > >> >> > > > >> > > access to set the timestamp? Presumably this will
> be a
> > > new
> > > >> >> field
> > > >> >> > > in
> > > >> >> > > > >> > > ProducerRecord, right? If so then any user can set
> the
> > > >> >> > timestamp,
> > > >> >> > > > >> right?
> > > >> >> > > > >> > > I'm not sure you answered the questions around how
> > this
> > > >> will
> > > >> >> > work
> > > >> >> > > > for
> > > >> >> > > > >> MM
> > > >> >> > > > >> > > since when MM retains timestamps from multiple
> > > partitions
> > > >> >> they
> > > >> >> > > will
> > > >> >> > > > >> then
> > > >> >> > > > >> > be
> > > >> >> > > > >> > > out of order and in the past (so the
> > > >> >> max(lastAppendedTimestamp,
> > > >> >> > > > >> > > currentTimeMillis) override you proposed will not
> > work,
> > > >> >> right?).
> > > >> >> > > If
> > > >> >> > > > we
> > > >> >> > > > >> > > don't do this then when you set up mirroring the
> data
> > > will
> > > >> >> all
> > > >> >> > be
> > > >> >> > > > new
> > > >> >> > > > >> and
> > > >> >> > > > >> > > you have the same retention problem you described.
> > > Maybe I
> > > >> >> > missed
> > > >> >> > > > >> > > something...?
> > > >> >> > > > >> > lastAppendedTimestamp means the timestamp of the
> message
> > > that
> > > >> >> last
> > > >> >> > > > >> > appended to the log.
> > > >> >> > > > >> > If a broker is a leader, since it will assign the
> > > timestamp
> > > >> by
> > > >> >> > > itself,
> > > >> >> > > > >> the
> > > >> >> > > > >> > lastAppenedTimestamp will be its local clock when
> append
> > > the
> > > >> >> last
> > > >> >> > > > >> message.
> > > >> >> > > > >> > So if there is no leader migration,
> > > >> max(lastAppendedTimestamp,
> > > >> >> > > > >> > currentTimeMillis) = currentTimeMillis.
> > > >> >> > > > >> > If a broker is a follower, because it will keep the
> > > leader's
> > > >> >> > > timestamp
> > > >> >> > > > >> > unchanged, the lastAppendedTime would be the leader's
> > > clock
> > > >> >> when
> > > >> >> > it
> > > >> >> > > > >> appends
> > > >> >> > > > >> > that message message. It keeps track of the
> > > lastAppendedTime
> > > >> >> only
> > > >> >> > in
> > > >> >> > > > >> case
> > > >> >> > > > >> > it becomes leader later on. At that point, it is
> > possible
> > > >> that
> > > >> >> the
> > > >> >> > > > >> > timestamp of the last appended message was stamped by
> > old
> > > >> >> leader,
> > > >> >> > > but
> > > >> >> > > > >> the
> > > >> >> > > > >> > new leader's currentTimeMillis < lastAppendedTime. If
> a
> > > new
> > > >> >> > message
> > > >> >> > > > >> comes,
> > > >> >> > > > >> > instead of stamp it with new leader's
> currentTimeMillis,
> > > we
> > > >> >> have
> > > >> >> > to
> > > >> >> > > > >> stamp
> > > >> >> > > > >> > it to lastAppendedTime to avoid the timestamp in the
> log
> > > >> going
> > > >> >> > > > backward.
> > > >> >> > > > >> > The max(lastAppendedTimestamp, currentTimeMillis) is
> > > purely
> > > >> >> based
> > > >> >> > on
> > > >> >> > > > the
> > > >> >> > > > >> > broker side clock. If MM produces message with
> different
> > > >> >> > > LogAppendTime
> > > >> >> > > > >> in
> > > >> >> > > > >> > source clusters to the same target cluster, the
> > > LogAppendTime
> > > >> >> will
> > > >> >> > > be
> > > >> >> > > > >> > ignored re-stamped by target cluster.
> > > >> >> > > > >> > I added a use case example for mirror maker in KIP-32.
> > > Also
> > > >> >> there
> > > >> >> > > is a
> > > >> >> > > > >> > corner case discussion about when we need the
> > > >> >> > max(lastAppendedTime,
> > > >> >> > > > >> > currentTimeMillis) trick. Could you take a look and
> see
> > if
> > > >> that
> > > >> >> > > > answers
> > > >> >> > > > >> > your question?
> > > >> >> > > > >> >
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > My main motivation is that given that both Samza and
> > > Kafka
> > > >> >> > streams
> > > >> >> > > > are
> > > >> >> > > > >> > > doing work that implies a mandatory client-defined
> > > notion
> > > >> of
> > > >> >> > > time, I
> > > >> >> > > > >> > really
> > > >> >> > > > >> > > think introducing a different mandatory notion of
> time
> > > in
> > > >> >> Kafka
> > > >> >> > is
> > > >> >> > > > >> going
> > > >> >> > > > >> > to
> > > >> >> > > > >> > > be quite odd. We should think hard about how
> > > client-defined
> > > >> >> time
> > > >> >> > > > could
> > > >> >> > > > >> > > work. I'm not sure if it can, but I'm also not sure
> > > that it
> > > >> >> > can't.
> > > >> >> > > > >> Having
> > > >> >> > > > >> > > both will be odd. Did you chat about this with
> > > Yi/Kartik on
> > > >> >> the
> > > >> >> > > > Samza
> > > >> >> > > > >> > side?
> > > >> >> > > > >> > I talked with Kartik and realized that it would be
> > useful
> > > to
> > > >> >> have
> > > >> >> > a
> > > >> >> > > > >> client
> > > >> >> > > > >> > timestamp to facilitate use cases like stream
> > processing.
> > > >> >> > > > >> > I was trying to figure out if we can simply use client
> > > >> >> timestamp
> > > >> >> > > > without
> > > >> >> > > > >> > introducing the server time. There are some discussion
> > in
> > > the
> > > >> >> KIP.
> > > >> >> > > > >> > The key problem we want to solve here is
> > > >> >> > > > >> > 1. We want log retention and rolling to depend on
> server
> > > >> clock.
> > > >> >> > > > >> > 2. We want to make sure the log-assiciated timestamp
> to
> > be
> > > >> >> > retained
> > > >> >> > > > when
> > > >> >> > > > >> > replicas moves.
> > > >> >> > > > >> > 3. We want to use the timestamp in some way that can
> > allow
> > > >> >> > searching
> > > >> >> > > > by
> > > >> >> > > > >> > timestamp.
> > > >> >> > > > >> > For 1 and 2, an alternative is to pass the
> > log-associated
> > > >> >> > timestamp
> > > >> >> > > > >> > through replication, that means we need to have a
> > > different
> > > >> >> > protocol
> > > >> >> > > > for
> > > >> >> > > > >> > replica fetching to pass log-associated timestamp. It
> is
> > > >> >> actually
> > > >> >> > > > >> > complicated and there could be a lot of corner cases
> to
> > > >> handle.
> > > >> >> > e.g.
> > > >> >> > > > >> what
> > > >> >> > > > >> > if an old leader started to fetch from the new leader,
> > > should
> > > >> >> it
> > > >> >> > > also
> > > >> >> > > > >> > update all of its old log segment timestamp?
> > > >> >> > > > >> > I think actually client side timestamp would be better
> > > for 3
> > > >> >> if we
> > > >> >> > > can
> > > >> >> > > > >> > find a way to make it work.
> > > >> >> > > > >> > So far I am not able to convince myself that only
> having
> > > >> client
> > > >> >> > side
> > > >> >> > > > >> > timestamp would work mainly because 1 and 2. There
> are a
> > > few
> > > >> >> > > > situations
> > > >> >> > > > >> I
> > > >> >> > > > >> > mentioned in the KIP.
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > When you are saying it won't work you are assuming
> > some
> > > >> >> > particular
> > > >> >> > > > >> > > implementation? Maybe that the index is a
> > monotonically
> > > >> >> > increasing
> > > >> >> > > > >> set of
> > > >> >> > > > >> > > pointers to the least record with a timestamp larger
> > > than
> > > >> the
> > > >> >> > > index
> > > >> >> > > > >> time?
> > > >> >> > > > >> > > In other words a search for time X gives the largest
> > > offset
> > > >> >> at
> > > >> >> > > which
> > > >> >> > > > >> all
> > > >> >> > > > >> > > records are <= X?
> > > >> >> > > > >> > It is a promising idea. We probably can have an
> > in-memory
> > > >> index
> > > >> >> > like
> > > >> >> > > > >> that,
> > > >> >> > > > >> > but might be complicated to have a file on disk like
> > that.
> > > >> >> Imagine
> > > >> >> > > > there
> > > >> >> > > > >> > are two timestamps T0 < T1. We see message Y created
> at
> > T1
> > > >> and
> > > >> >> > > created
> > > >> >> > > > >> > index like [T1->Y], then we see message created at T1,
> > > >> >> supposedly
> > > >> >> > we
> > > >> >> > > > >> should
> > > >> >> > > > >> > have index look like [T0->X, T1->Y], it is easy to do
> in
> > > >> >> memory,
> > > >> >> > but
> > > >> >> > > > we
> > > >> >> > > > >> > might have to rewrite the index file completely. Maybe
> > we
> > > can
> > > >> >> have
> > > >> >> > > the
> > > >> >> > > > >> > first entry with timestamp to 0, and only update the
> > first
> > > >> >> pointer
> > > >> >> > > for
> > > >> >> > > > >> any
> > > >> >> > > > >> > out of range timestamp, so the index will be [0->X,
> > > T1->Y].
> > > >> >> Also,
> > > >> >> > > the
> > > >> >> > > > >> range
> > > >> >> > > > >> > of timestamps in the log segments can overlap with
> each
> > > >> other.
> > > >> >> > That
> > > >> >> > > > >> means
> > > >> >> > > > >> > we either need to keep a cross segments index file or
> we
> > > need
> > > >> >> to
> > > >> >> > > check
> > > >> >> > > > >> all
> > > >> >> > > > >> > the index file for each log segment.
> > > >> >> > > > >> > I separated out the time based log index to KIP-33
> > > because it
> > > >> >> can
> > > >> >> > be
> > > >> >> > > > an
> > > >> >> > > > >> > independent follow up feature as Neha suggested. I
> will
> > > try
> > > >> to
> > > >> >> > make
> > > >> >> > > > the
> > > >> >> > > > >> > time based index work with client side timestamp.
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > For retention, I agree with the problem you point
> out,
> > > but
> > > >> I
> > > >> >> > think
> > > >> >> > > > >> what
> > > >> >> > > > >> > you
> > > >> >> > > > >> > > are saying in that case is that you want a size
> limit
> > > too.
> > > >> If
> > > >> >> > you
> > > >> >> > > > use
> > > >> >> > > > >> > > system time you actually hit the same problem: say
> you
> > > do a
> > > >> >> full
> > > >> >> > > > dump
> > > >> >> > > > >> of
> > > >> >> > > > >> > a
> > > >> >> > > > >> > > DB table with a setting of 7 days retention, your
> > > retention
> > > >> >> will
> > > >> >> > > > >> actually
> > > >> >> > > > >> > > not get enforced for the first 7 days because the
> data
> > > is
> > > >> >> "new
> > > >> >> > to
> > > >> >> > > > >> Kafka".
> > > >> >> > > > >> > I kind of think the size limit here is orthogonal. It
> > is a
> > > >> >> valid
> > > >> >> > use
> > > >> >> > > > >> case
> > > >> >> > > > >> > where people only want to use time based retention
> only.
> > > In
> > > >> >> your
> > > >> >> > > > >> example,
> > > >> >> > > > >> > depending on client timestamp might break the
> > > functionality -
> > > >> >> say
> > > >> >> > it
> > > >> >> > > > is
> > > >> >> > > > >> a
> > > >> >> > > > >> > bootstrap case people actually need to read all the
> > data.
> > > If
> > > >> we
> > > >> >> > > depend
> > > >> >> > > > >> on
> > > >> >> > > > >> > the client timestamp, the data might be deleted
> > instantly
> > > >> when
> > > >> >> > they
> > > >> >> > > > >> come to
> > > >> >> > > > >> > the broker. It might be too demanding to expect the
> > > broker to
> > > >> >> > > > understand
> > > >> >> > > > >> > what people actually want to do with the data coming
> in.
> > > So
> > > >> the
> > > >> >> > > > >> guarantee
> > > >> >> > > > >> > of using server side timestamp is that "after appended
> > to
> > > the
> > > >> >> log,
> > > >> >> > > all
> > > >> >> > > > >> > messages will be available on broker for retention
> > time",
> > > >> >> which is
> > > >> >> > > not
> > > >> >> > > > >> > changeable by clients.
> > > >> >> > > > >> > >
> > > >> >> > > > >> > > -Jay
> > > >> >> > > > >> >
> > > >> >> > > > >> > On Thu, Sep 10, 2015 at 12:55 PM, Jiangjie Qin <
> > > >> >> j...@linkedin.com
> > > >> >> > >
> > > >> >> > > > >> wrote:
> > > >> >> > > > >> >
> > > >> >> > > > >> >> Hi folks,
> > > >> >> > > > >> >>
> > > >> >> > > > >> >> This proposal was previously in KIP-31 and we
> separated
> > > it
> > > >> to
> > > >> >> > > KIP-32
> > > >> >> > > > >> per
> > > >> >> > > > >> >> Neha and Jay's suggestion.
> > > >> >> > > > >> >>
> > > >> >> > > > >> >> The proposal is to add the following two timestamps
> to
> > > Kafka
> > > >> >> > > message.
> > > >> >> > > > >> >> - CreateTime
> > > >> >> > > > >> >> - LogAppendTime
> > > >> >> > > > >> >>
> > > >> >> > > > >> >> The CreateTime will be set by the producer and will
> > > change
> > > >> >> after
> > > >> >> > > > that.
> > > >> >> > > > >> >> The LogAppendTime will be set by broker for purpose
> > such
> > > as
> > > >> >> > enforce
> > > >> >> > > > log
> > > >> >> > > > >> >> retention and log rolling.
> > > >> >> > > > >> >>
> > > >> >> > > > >> >> Thanks,
> > > >> >> > > > >> >>
> > > >> >> > > > >> >> Jiangjie (Becket) Qin
> > > >> >> > > > >> >>
> > > >> >> > > > >> >>
> > > >> >> > > > >> >
> > > >> >> > > > >>
> > > >> >> > > > >
> > > >> >> > > > >
> > > >> >> > > >
> > > >> >> > >
> > > >> >> > >
> > > >> >> > >
> > > >> >> > > --
> > > >> >> > > -- Guozhang
> > > >> >> > >
> > > >> >> >
> > > >> >>
> > > >> >
> > > >> >
> > > >>
> > >
> > >
> >
>
